Generally, display devices are required to have as wide a viewing angle as possible so that a clear image can be viewed from all viewing angles. In liquid crystal display devices which have been in widespread use, liquid crystal itself has a viewing angle dependency. On this account, in particular, various technological developments have been promoted for making the viewing angle wider.
However, depending on a use environment, there is a case that it is favorable for a display device to have a narrow viewing angle so that only a user can view display contents. An electronic device, such as a laptop type personal computer, a portable information terminal (PDA: Personal Digital Assistant), or a portable phone, in particular, is more likely to be used in a place (e.g., in a train, airplane, etc.) where general public can be present. Under such a use environment, it is desirable that a viewing angle of a display device be narrow because the user does not wish the display contents to be viewed by others near to the user, in view of preservation of confidentiality and/or privacy protection. Thus, the demand has been recently increased for a liquid crystal display device in which the viewing angle can be switched between a wide viewing angle and a narrow viewing angle in accordance with a situation in which the liquid crystal display device is used. Such demand is not limited to liquid crystal display devices. Instead, it is a problem shared by any display devices.
For example, Patent Document 1 (later described) proposes the following technique, in order to meet such a demand. Specifically, the Patent Document 1 discloses a technique in which a retardation control device is provided in addition to a display device for displaying an image. According to the technique, a voltage to be applied to the retardation control device is controlled so that a display device has a change in a viewing angle feature. The Patent Document 1 adopts a liquid crystal display device, serving as the retardation control device, whose liquid crystal is chiral nematic liquid crystal, homogeneous liquid crystal, or randomly aligned nematic liquid crystal, for example.
The Patent Document 1 describes that it is possible to switch the viewing angle between a wide viewing angle and a narrow viewing angle by using the liquid crystal display device for controlling retardation. However, the switching of the viewing angle between the wide viewing angle and the narrow viewing angle is not always necessary.
In a case where the viewing angle can be switched between the wide and the narrow viewing angles in a display device, the display device has a complex arrangement. As such, in view of cost reduction, a display device has been demanded in which viewing angles can be narrowed though not being able to be switched between the wide and narrow viewing angles.
For example, Patent Document 2 (later described) discloses a technique in which a viewing angle is narrowed without being switched between the wide and narrow viewing angles. The Patent Document 2 discloses a viewing field control sheet, which substitutes for the retardation control device capable of switching the viewing angle between the wide and narrow viewing angles. As shown in FIG. 19, a louvered film 102 serving as the viewing field control sheet is stacked on top of a liquid crystal panel 101 that has a liquid crystal cell 111 made of TN liquid crystal. As shown in FIG. 20, the louvered film 102 includes (i) base material sections 121 made of a light transmission material and (ii) light absorption barriers 122 made of a light absorption material and formed in a louvered manner. The light absorption barriers 122, made of the light absorption material, have a refraction index smaller than that of the base material sections 121 made of light transmission material. The louvered film 102 blocks outgoing of light that has an incident angle of a particular angle or more. Thus, it is possible to realize the viewing field control sheet that brings about a peek prevention effect.
The louvered film 102 disclosed in the Patent Document 2 has recently become a mainstream in viewing angle control panels that does not switch a viewing angle between the wide viewing and narrow viewing angles.
(Patent Document 1)
Japanese Unexamined Patent Application Publication, Tokukai-hei, No. H11-174489 (published on Jul. 2, 1999)
(Patent Document 2)
Japanese Unexamined Patent Application Publication, Tokukai, No. 2000-137294 (published on May 16, 2000)